The invention relates in general to the verifying of signals, notably of signals with various features, whereby each of these features may be subject to quantitive variability. Such signals may originate from differing signal sources. The features may, for example, involve frequencies, amplitudes, pulse shapes or the time-dependency of a signal. The frequencies may occur at varying amplitudes or over varying periods. The amplitudes may occur for varying periods or at different intervals. The pulse shapes may vary in amplitude, slope, or the number of repetitions of the same pulse. The variability may be caused by random effects and also by slow changes, e.g. aging. Both effects may occur together. Examples of such signals needing verifying are those obtained during character recognition, sound analysis and speaker verification.
By verifying here is meant a test whether or not a signal originates from a pre-indicated source. Such a problem arises in the classification of signals where a test is to be made to find out whether a signal belongs to a pre-indicated group of classes and, if so, to which one. In both cases the features or values of the features occurring in the class or classes is first determined by means of a number of exemplary samples and these values must be stored, so that they can subsequently be compared with the values of the features of the signal to be verified. Here, the individual values of the features may be stored either directly or in a derived form, e.g. as an average with variance.